Semiconductor and micromechanical systems are formed on substrates, such as silicon wafers. A complex sequence of operations involving depositing, etching, shaping, patterning and washing are applied to the substrate to form the tiny structures that form the semiconductor and micromechanical parts on the substrate. These structures are made smaller and closer together in order to reduce cost. The smaller structures require less material, less power to operate, and less space to house. The smaller structures are also often faster than larger structures and may have many more advantages.
In order to make smaller structures, the fabrication processes must be more precise. Every aspect of the process is improved over time to enable smaller structures. Many of the fabrication processes, such as electron beam deposition, plasma deposition, plasma-enhanced chemical vapor deposition (PECVD), resist stripping, and plasma etching, etc. are affected by the temperature of the silicon wafer. If the temperature of the wafer in one location is different from that in another location, then the result of the process will be different in the different locations. In addition, if the temperature is different from the temperature for which the process was designed, then the results of the process will not be what was designed. As a result, temperature variations during fabrication may cause some structures to work poorly or even be inoperable.
The temperature of a substrate in a processing chamber can be measured using an infrared camera or a heat sensor on the substrate. In some cases a special wafer is used that has one or more thermal sensors and that store temperatures in a memory during a test process. A process is performed with the special wafer in the chamber and then the process is adjusted based on the measured temperatures.